Light aluminum alloy



Patented Feb- UNITED STATES PATENT OFFICE KAI BOSSHARD, OF NEUHAUBEN, SWITZERLAND, ASSIGNOB'TO ALUMINIUM INDUS- TRIE AKTIENGESELLSGHAFT, OI NEUHAUSEN, SWITZERLAND, A JOINT-STOCK GOM- IPANY OF SWITZERLAND LIGHT ALUMINUM ALLOY No Drawing. Application filed November 25, 1831, Serial'No. 577,401, and in Germany December 3, 1980.

This invention is a new and useful light aluminum alloy, available either for casting or working purposes.

The main object of the invention is to afford a light aluminum alloy which can be subjected to suitable heat treatment to improve its properties of tensile strength or hardness or both, and which alloy also, possesses the property of high resistance to corrosion, for example from exposure to air which is moist and briny. Heretofore light aluminum alloys well adapted to heat treatment have possessed but low resistance to corrosion. On the other hand alloys having corrosion resisting properties have been but ill adapted to heat treatment. With the present improvement an alloy is afforded which possesses the property of lightness, is heat treatable to strengthen and harden the same, and is well constituted to resist corrosion. Further objects and advantages of the invention will be explained in the hereinafter following description of illustrative embodiments thereof or will be understood to those conversant with the subject.

The present alloy is composed chiefly of aluminum, which may substantially exceed 90% of the total weight. Certain "traces of usual impurities are permissible so long as they do not exceed the limit of such impurities as permitted in commercially pure aluminum, such as traces of copper, silver, tin. nickel, cobalt, iron, chromium, etc.

The components which chiefly insure heat treatability are small percentages of magnesium and of manganese, together with a percentage of s1l1con in an amount and for a purpose which will be below further described. These components may be referred followed by an explanation thereof, and thereafter a recital of certain illustrative modifications within the scope of the improve tnent. The formula or composition may be as follows, stated in percentages, by weight:

Magnesium ..0.2 to 1.0 Manganese 0.2 to 1.0 I Silicon up to 5.0 Antimony and/or cadmium and/or arsenic up to 2.0 Aluminum balance In explanation of the above formula, the first three components or group represent the strengthening or hardening influence, this being in a general way well known. For the purpose of the present improvement, however, the following condition is important. The silicon has been stated as being used up to 5%, but the proportion of silicon, below such 5% should nevertheless be suflioiently great, for exam le above 0.5%, that the entire content 0 both magnesium and manganese become and are chemically combined with the silicon. By this proportion of silicon it is insured that the ma esium will exist in the finished alloy as si icid of magnesium only, and not in any other form,

and it will be as finely distributed and divided so ,in the same alloy of the heat treatment components and the non-corrosion components is the basic thought back of the present invention.

The second group content, comprising antimony and/or cadmium and/or arsenic may consist of any one only of the elements in this group, or two of them or all of them, the total percentage by weight thereof to be maintained below 2%, being variable however, for example between 0.05 and 1.5% in accordance with the'particular component used or with the degree of resistanceto corrosion which may be demanded. An excess or deficiency is a detriment to the property desired.

Among modifications falling within the described invention is the addition to the aforesaid second group of metals or elements of another metal, bismuth, and as with the others of this group bismuth may be used alone, or may be combined with any one or more or all of the others of the group, so that the total percentage of this group in the final alloy substantially does not exceed 2%. It has been further discovered that an advantage pertains to the addition of bismuth to the formula in that this component also improves substantially the efiect of heat treatment of the alloy.

The improved alloy set forth in the above formula may be subjected to heat treatment, for example in the usual manner of heat treatments, by annealing the article or product at a temperature between 500 C. and 600 0.,

followed by quenching and then artificial agingCat a temperature between 100 C. and 200 As a result of a number of tests of rolled or sheet products prepared "from this improved alloy, the average tensile strength has been ascertained as amounting to 34 to 36 kilograms per square millimeter. For cast products or bars in which the silicon content suitably exceeds 1.5% an average tensile strength of about 30 kgs. per square mm. is obtained. When a substantial percentage of bismuth is included in the composition the tensile strength may average as high as 39 to 42 kgs. per square mm. for sheet material.

The resulting alloys and products possess good resistance to corrosion not only by moist and briny air, but also by hydrochloric acid, or by either diluted or concentrated nitric acid, or by fruit acids and the like. The alloys hereof moreover are found to have an increased resistance against corrosion by alkaline agents. I

The alloyingof the described components may be according to known practise, with due regard to the order of combining the components, the temperatures and the mode of mixing and pouring the product.

There has thus been described a light aluminum alloy according to this invention possessing the properties and advantages referred to. Since matters of proportion, ingredient and method of alloying may be varied within the principles of the invention it is not intended to limit the invention to such matters except to the extent set forth in the appended claims.

What I claim is:

1. A light alloy of aluminum resistant to corrosion and heat treatable for strength or .light aluminum alloy as in claim, 1, further characterized by the fact that the same contains bismuth instead of or together with one or more of the elements of the group consistin of antimony, cadmium and arsenic,

the W ole amount of bismuth and the elements of said group not exceeding 2.0 per cent.

3. A heat treatable light alloy of aluminum resistant to corrosion consisting substantially Wholly of aluminum but characterized by a content of about 0.2 to 1.0 per cent of magnesium, about 0.2 to 1.0 per cent of manganese, about 0.05 to 2 per cent of one or more of the elements of the group consisting of cadmium, antimony, arsenic and bismuth, and with a proportion of silicon not exceeding about 5.0 per cent but at least so high that the whole content of manganese and magnesium is combined with silicon.

4. A light alloy of aluminum which is both heat treatable and resistant to corrosion, characterized by a content of 0.2 to 1.0 parts of magnesium, 0.2 to 1.0 parts of manganese, 0.05 to 2 parts of one or more of the elements of the group consisting of cadmium, an-

timony, arsenic and bismuth, with a propor- I tion of silicon not exceeding about 5.0 parts 

